Project Summary/Abstract Virus-host interactions play an essential role in many stages of the viral lifecycle, including cell entry. Understanding the mechanisms that facilitate virus entry is necessary for developing effective therapies that prevent infection by important human pathogens. Mammalian orthoreovirus (reovirus), a well-established model system for studying the entry mechanisms of nonenveloped viruses, undergoes a series of regulated structural transitions that culminate in penetration of host membranes and delivery of the viral genetic material. One of these conformational changes, infectious subviral particle (ISVP)-to-ISVP* conversion, is promoted by myr-1N, a myristoylated peptide that is released from the virus particle during entry. Moreover, specific lipids optimize the ISVP* promoting activity of myr-1N. Thus, the interplay between reovirus and lipids reveals a distinct virus-host interaction in which membranes can actively participate in the entry process of a nonenveloped virus. The two specific aims that are outlined in this proposal utilize a multidisciplinary approach to investigate the molecular mechanisms that regulate lipid-facilitated reovirus entry. In Specific Aim 1, biochemical and imaging techniques will be used to define the biophysical properties that underlie lipid- mediated ISVP-to-ISVP* conversion and membrane penetration. In Specific Aim 2, genetic techniques will be used to identify the specific residues within lipid-associated myr-1N that are necessary initiating infection. The proposed research will contribute significant knowledge to the strategies that nonenveloped viruses can use to interact with host cells and how these interactions aid in the establishment of a productive infection.